Adsorption process



Jan. 19, 1954 R. P; CAHN ET AL 2,666,500

ADsoRPTIoN PROCESS Filed Oct. 16, 1950 2 Sheets-Sheet 1 35 To LIF-r GASC -Pao-:mc:- SmE STREAM 3 1 1 FT @A5 (TAH. GAS) @ober-t, P. {chtz LewisD. Etherirzgton n y l M Umborria nvenbors Jan. 19, k1954 R, P CAHN ET AL2,666,500

ADSORPTION PROCESS VFiled oct. 16, 195o 2 sheets-sheet 2 TQ F-^CTON^TN)(2O (LIF-'T LIQUID A+C. LIQUIDJ 'Erb Anskolbaw.

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55) (1,? 9- T 4 WAsI-I LIQUIDS SOL-IDS f 'ZZS 1 P" I.' c; I-' 2 bg MCltfborrzcg Patented Jan.L 19, 1954 UNITED STATES PATENT crema Robert t.IQ; n Ether..

ngtonl, Cral.lford,A N- J assisilcrsi. t0 Standard Oil DevelopmentCompany, a corporation of Delaware Arrl'icatinnctcber 16, 1950iScrialNOf- 13.0292

` nclaims. (o1. iss-114.2)A

This invention is concerned with an improved adsorptive separationprocess` in which the bot-.- toms product or heaviest componentv of themix: ture, undergoing separation partially described from thecirculatingv adsorbent. and, more completely desorbed from a. remainingfraction of the adsorbent. More particularly the. invention relates toaprocess, for reducing the/losses of the heaviest components of the,mixture undergoing separation inr a( adsorption process, and in so doingto minimize, desorption. reouirements and vreduce contamination. oflighter productsby the heaviest product.

It is an object of" this. invention to. provide. a. highly stripped:adsorbentv without. an. increasey in the overall strippingrequiremerits,Y of ,an ad-4 sorption-.desorption process for. theseparation of uidmixtures. It is an object o thisinvention to reduce thelossof bottomsv product; from the overhead product lby means ot this.highly stripped adsorbent. It is, anA object of thisv invention tovprovide a process for the productiony of a highly purifiedintermediate.' fraction. from. a mixture containing slightly,I mediumand. strongly. adsorbable. fractions, by means of this highly strippedadsorbent. It isa further obiect. of this invention to provide a highlystripped adsorbent to. a regeneration or high temperature heating. step.in order to, reduce the loss of heavy component by combustion orotherwise.

l These and other objectsv of. the. invention will. be, ailliarentyfrom. the description to( follow.

The process of separating. components of mixtures, both liquid andgaseous,l by means. of solid adsorbents hasbeen Well described., It isknown that components of a mixture having varying. ydegrees ofadsorbability may be separated by contacting the mixture with a solidVadsorbent. whereby the more adolbablecomponentis ade sor-bed` by theSolid in. preference to.; the.. less adsorbable component. .The`solidfis, then. treated to recover the more adsorbahle componenttherefrom in. a process called'y desorption.. The. lat?. ter is. usuallyaccomplished. by heat. and/or. stripping with steam or inert gas or by.means of washing. with` hydrocarbons oxygenatedr hydro.- carbons orWater in` liquid' for-m. It is well known thatvv gaseous, 01.' liquid.hydrocarbon mixtures arey separated into, their. coinocuontsy by..tlcaltnsf, them inv intimate contact( solid, adorbcrlts, particularly.activated carbon,` Silica gel', ctc... In, general itmaory basaidthattheactivated arbonsseparate, the. hydrocarbons. roughly by molecularWeight, thev higher, molecularv weight components of. the hydrcnarhqumixture .beine 2 moreselect'ively adsorbedby thecarbon. "On the otherhand silicav gel usually displays' an` affinity' for the olenic ormoreunsaturated typein prererence to the less unsaturated or paramnio type.

In the selective separation oi hydiccarbons by contactingL a .gaseousstream comprising them Willact'ivated. carbon in a cyclic ,process inwhich the carbon saturated with. adsorbed components is desorbed. bystripping, e. g.. with steam. and heat and returnedv tov the adsorptionZone, as will be, more fully described. below, it .is usually not.economically Y'feasible to completely `remove the adsorbed hydrocarbonskfrom the total-V Girculated activated. carbon in the desorptionZOne@ Acertain amountt ofA thesev hydrocarbons, thereg fore., are recycledwitlrV the adsorbent tothetop of the4 adsorption zone and are vlosttothelight components or tail gas by partiel strippingv of theadsorbent. by the., overhead product, Order to avoidl losa, Dart of theacllsorbent preferably labout 2 0, weight per cent orv there abouts,leaving the high temperature steam stripping or desorption zone. is.contacted with the total steam in a separate vessel@ separate.

stage or stages: prior to injection of thisI samev steam into thedesorption section proper. 'Ifhis additional stripping operation`removes- .more completely the. heavy component and leaves a charcoalsubstantially` free of adsorbed bottoms components. Thisv speciallystripruedv charcoal is highly suitable for return tothe adsorptionsys-,-` tem at. points Where.4 its effectiveness; canY bemosti highlyutilized.. I t, is employed to scrub.Y the tailgas emerging fromtheadsorption Zone whereby it completely adsorhs theheavy componentspresent. in the tail. gas. It is alsoemployed masocondary adsorber tostrip, unavoidable equilibriumquantities of the heavier component. from;aprirmary adsorber sidestream thereby permitting they production of a.highly purified intermediate component fraction. Y a

The invention will bev more. readily understood when thed'escription ofthe same is.A read in confnection with the drawings in which. thefigures-j represent elevationviews in. crosssectionof; equipment adaptedto carry out the process.v Figure l represents a. flowI plan` for.carrying. out" the; invention inf. a1 vapor-solid system; While Eigure2. represents. a liquid-solid systemg Referring to. Figure. 1 ofthadrawins mimeifal l .represents an. adsorption-desorptioncomme.supplied'A withl a feed line 2 `dverheafd. product.' draw-fort" pipes.3, and Ii l middlelsidestream.. prod u cti draw-off; pipes 23;. and Z8.,lower bottoms product draw-off pipe 5, a heater 6, a steam entry pipe l,solids entry pipes 4, I5 and 29, and solids draw-oit pipes 8 and I0. Aseparate desorption vessel e is provided to receive a minor amount orthe solids leaving vessel I Via pipe 8. The stripping vessel S isequipped with a pipe I6 for admittance of stripping gas.

Employing the equipment of the drawing, the invention will beillustrated with respect to the resolution by means of charcoaladsorption of a gaseous hydrocarbon mixture containing a light fraction,namely methane and attendant noncondensible gases such as hydrogen,nitrogen, etc.,

an intermediate fraction consisting of C2 hydrocarbons, viz., ethane andethylene, and a heavy or bottoms product fraction consisting of C3 andheavier hydrocarbons, viz., propane, propylene, butane, butenes, etc. Agaseous mixture of such composition is introduced into vessel I via pipe2 at apoint slightly above the mid-section thereof.' The bulk of thecirculated activated charcoal adsorbent is introduced into the vessel Iat the top thereof via line I5 with recycle lift gas obtained throughline II. Vessel I may be constructed to handle iluidized charcoal inwhich event true countercurrent flow of charcoal and feed gas iseffected by providing the adsorption vessel with perforated plates,bubble-capped plates, baffles, or stationary packing. The plates areequipped with weirs and downcomers to facilitate ow of the charcoal froman upper to a lower plate consecutively down the tower. The plates areso constructed as to enable upwardly dowing gases to flow through theopenings thereof while not allowing passage of the charcoal downwardlytherethrough. The charcoal therefore builds up on the plates until thelevel of the weir is reached whereupon the char flows down the downcomerto the plate immediately below. In such an operation finely-divideduidized charcoal of 50-200 micron particle size is preferably employedand the charcoal is iiuidized by the process gas undergoing separation.Alternatively, the adsorption vessel may be operated as a soaker-typevessel in which charcoal is packed in the tower and allowed to gravitateslowly at a xed rate from the top to the bottom of the tower. In thisevent charcoal of approximately 10 to 30 mesh particle size 1s employed.The adsorption tower may be visualized as consisting of three zones ineach of which a specific function is performed. The zone above the gasfeed line 2 is the adsorption zone proper, while the zone immediatelybelow the gas feed line and extending to the bottoms product draw-offline 5 is a rectication Zone. The zone below the C3 and heavier productdraw-off line extending to the bottom of the vessel and containing theheater and steam entry lines is the desorption zone proper.

Returning to the drawing the charcoal descending the towercountercurrently contacts the upwardly rising bases introduced Via pipe2. The charcoal more selectively adsorbs theheavier components of thegaseous feed so that the C2, C3, and heavier components arepreferentially adsorbed, wlth relatively small equilibrium quantities ofthe methane and lighter gases, while the bulk of the latter pass up thetower and leave the vessel via line 3. The charcoal containing theadsorbed components passes down the tower past the feed Plpe into aportion of the rectification Zone between lines 2 and 28 wherein thecharcoal is re- ;duxed by predominantly C2 and heavier hydrocarbonvapors passing up the tower from the de- SOrption zone as will befurther @.Xyllined below- These vapors tend to release methane from thecharcoal in the upper portion of the rectification zone and arethemselves readsorbed. A Cz-hydrocarbon vapor stream, containingessentially no methane but unavoidable equilibrium amounts of C3 andheavier hydrocarbons is removed from the vessel I via pipe 28 or viapipe 23, as described further below. The charcoal continues its descentthrough the remaining portion of the rectification Zone between lines 28and 5 wherein reuxed C3 and heavier hydrocarbon desorbs the intermediate=C2 fractions while C3 and heavier hydrocarbons are readsorbed. The charthen reaches the bottom portion or partial desorption zone below line 5and containing heater 6. In this region the charcoal is heated toapproximately 45o-550 F. to partially release the adsorbed componentsthereon, chiefly the C3 and higher hydrocarbons. Assisting the heat inthis regard is the stripping action of steam or other gas introducedinto the bottom of the vessel via line 1. The released Cs and heavierhydrocarbons are removed from the tower via line 5 although a portion ofthem pass up the tower to serve as reflux as previously mentioned. Theaction of the heat and stripping steam removes the bulk of the adsorbedC3 and heavier components from the charcoal, but does not completelystrip these components off the char. Now, a portion of the hot charcoalis removed from the desorption section via line s and introduced into asmaller stripping vessel S entering at a point near the top thereof.This vessel is likewise constructed and operated so as to providecountercurrent contact of charcoal and strip ping agent, e. g., steamentering the bottom of the vessel via line i6. The amount of charcoalintroduced into the vessel 9 is approximately 10-40 weight per cent ofthe total char leaving the adsorption vessel I. Preferably about 20weight per cent of the charcoal is introduced into vessel 9, dependinglargely on the feed gas composition and the total requirement ofspecially stripped char in the overall process. Here the Withdrawncharcoal is stripped with the total stripping steam prior to theintroduction of this same steam into the partial desorption sectionwhere the bulk of the desorption is performed, By this method part ofthe charcoal is contacted with the total steam and is thus morecompletely desorbed and representsamore purified char whose capacity forheavy hydrocarbon components has been more completely restored and willthus permit good clean-up operation for the removal of traces of heavycomponentr from other streams, where its presence is undesirable orwasteful. lt will be seen that if 4 mols of steam per 1000 lbs. of charis employed in the partial desorption section, then 2O mols per 1000lbs, of char will contact the 20% withdrawn charcoal in the vesselfS. Inthis manner the same overall amount of stripping steam is utilized butit is employed more efficiently. The total steam with desorbed C3 andheavier vapors leave vessel 5 via line 'l and is introduced into thedesorption section of vessel I to strip the total charcoal therein. Theless completely stripped char representing 60-96 weight per cent,preferably about 30 weight per cent, of the total charcoal circulatinginthe system is removed from vessel I via line I9, This char is returnedto the top of the adsorption zone by means of the lifting action of aportion of the light gases (tail gas) withdrawn from the tower I vialine II and repressured via blower I2. The

compressed gas picks up the hot charcoal as it emerges .fm 1511.3 DQOID.0f the Vessel Va line Eil f. and Vlifts itvi-a line i3 through coolerIi-.wherein the charcoal is cooled. down to atemperatureof approximately'100e20or Fa and.' then introduced via line I5; to the top of. theadsorption zone-oi tower I to repeat the adsorption cycle.

Returning now to the: stripping vessel 9' the;- hot, completely strippedcharcoal lsf. removed from. the vessel Via pipe I'If.V Disposition .ofthis char is determined by the manner in which.. the separation processis being carried out. A number of alternatives singly or together isemployed. If a highv Cierecovery is desi-redlpuried repres sured tailgasconsisting substantially of methane and lighter components: drawnAfrom pipe 22 via.- pipe 33% isintroduced via line- I-Bf to'. serve asliftgas to convey-the hot charcoal through cooler I9 and'line 20 toscrubber 2I-1. The coole-dfchar, at a temperature of about. 100s-200 F.,preferably about 125" enters scrubber 2.! atV a. point near the topthereof and ilows. downwardly through the vessel countercurrent to thehw drocarbon gas entering the bottom ci the vessel' from the-adsorptionvessel via line 3. Thechar, since it has beenspecially stripped of' C3and heavier hydrocarbons in stripper 9 is particularly adaptable to theC3 clean-up of the lean: gas emergingfrom the adsorption zone. The charpicks up some C2 and' particularly any C3 hydrocarbons present in thegas, leaving C1 and some Cas.- as substantially the only hydrocarboncomponents-of the purifledgas leaving the scrubber via. line 2,2'. Thechar reaching. the` bottom of4 the. tower contains some small amounts ofadsorbed C2 and Cs hydrocarbons andZ contains substantially the samespeciiic quantity of Cs.. per-unit char as the. char entering. vessel I.Vla line l5.. This charcoal, therefore, isremovedirom vessel 2|y vialine 4. and introduced` into. vessel I. at the topthereof where itmingles with the other char and repeats the-adsorption cycle.

In.l the event that the. process is: being.- operated' toobtain anintermediate component` ofi exftremely high purity another feature-of:the invert... tion is employed. Accordingvv to this modification a,sidestream adsorber 3l is employed,v and the C2. product draw-oil pipe23- is closed; off; 'A portion oif the highly stripped; char is'removed. from line IT: via line 24 and with the aidy of repressured`puried- Cahydrocarboir gas.; (from line 3:2).- isv lifted via line 2.5.-to cooler y2li to reduce the: char temperature to the proper adsorptionlevelof :loof-WL F., preferably about 12.59- F. The cool'- chariscarried through` pipe, 2linto adr sorber 3| entering atthe top thereof.The-chardescends the tower inthe same manner as` in; vesselsv 9, and 2l.A vapor' stream compris ing essentially only C2, C: and heaviercomponents is withdrawn: from a1 platein vessel t. below the-fecdpplate2. preferably-ata point where the concentration in. the; rising; vapor.has beenV reduced toa.very-low.V value and: allowed.- to passupwardly-into adsorberl. violino-218.. The. descending char adSor-bsthecountercurren-tly-` flowing gas ofthe heavier components, viz., Ca+

allowing a puriiied- C2.- streanrto emerse vialine 39... 'IheLdescending char is. returned.- via line 2.9 to; the mehr adsorption.vessel I- at; a. point below the point or vapor withdrawel.A tronil thevessel. At; this-peint the. charsr the main; tower. and the.sidestreamadsorber-aro ofI the-'same approx? mate-composition and.'descend through the-main.

tower I to undergo desorption aspreviouslifrecited. Also thestripped-char is. suitable for. high temperature-regeneration as anyother. eher used.- for this would result in a certain amount of.

TOI

:incomplete-.adsorptimr.

The@ process-l. described. permits the.- minimizingof-` C314--lossesif'ronr zthef system.. and assures; theattainment: crm-1ydesired.degree of. purity ofthe.

sidestream. product. without.- resorting to excessive amounts`oistripping.y steamor to;` an excessi-11e.` number` of plates; in' the.`desorptionsection-ofi .then-main adsorben-y Eor af highpurity C2;

product.anappreciableisafvings; instripping steam requirements canbeifrealized" at the expense ofa slightly' higher charY circulation.rate. due to the residual Cal.andheayier-componentsrecycled with the..bnl-lo of thezcirculating? char.. This can be carried;- oiitby-reducingrtheamountof stripping:

. of Figure 1 it should beborne in mind. that it isy possible-tocombine: vessels I, 9; and 2| into asingle unitary vessel withoutIentailing any changesirr the invention.

The process of the; invention is also adaptable to.A the separation ofliquidf mixtures in a liquidsolid: system.. For example.. thesepara-tion of a. mixture.-com-prisiirig.` a less adsorbable component Aandia more adsorbable-compcnent B employing charcoal asnthe'adsorbentist carried. out inthe eil.minuten-tv shownr irl` the flow-plan ofFigure 2. The liquid; eedi is introduced into vessel I via line 2 and iscontactedA with: solid adsorbent descending the. tower.. In.y thisoperation aL moving bed'.@granular-adsorbent is` employed, or a slurryof finely-divided. adsorbent. and the less adsorbable.- component; Ais.: suitable. The solid; in the main. adsorption sect-ion. 3.preferentially adsorbethe.; more-adsorbable component. B together withan equilibrium amount of. component A. The adsorbent passes down thevessel below the feed line into a rect-incation.y section 4- wherein thesolid; is: reiluxed4 with liquid. consisting substantie-1131 ofcomponent; B- entering the section via line 6. Component. B- displacescomponent A from the solid and the latter passes up the tower into aclean-upseetipnS whereinany remaining traces of component B-arescrubbedout by solid adsorbent circulatingirom the -top of the tower as will`be. relai-ted. below. The adsorbent saturated with liquid component Bpasses from vessel. I via. line 1: into-partial desorber 8 entering thetcp thereof. InA thisY vessel component B'V is partially desorloed`froml the solid in a physical operation-.emailing sweeping of the. solidwith a liquid; washL liquid: C: introduced. in. suicient vol!- ume vialine 9. Heat may be applied to the cesser toassistin.this-:operation it.desired. Wash liquid. is preferentially a. 'liquidi boiling lower thancomponents Aand- B- and-isless adsorbable than. either A1 or B.. Aliquid: stream of B and removed-i from vessel 8 via line It and is senttoa-.fractionation (not. shown). forseparation ot' B.- and-f C. The.latter.v is returned to the systemvia line. i5.. Part. oliy the streamisl removed via:v line Bfand serves-.asf reflux totherecticationsection. 4.-.. The.. partially desorbed. solid is. withydrawn fromvessel 8 via 1ine23 and is separated into two streams.- 'Ihe-,bulk ofthe solid (for eX- ample. 60-90 weight. per cent). is withdrawn vialine. Island'. reeirculated',L with. recycley lift. liduid. via. 2.I.'andafter cooling in. cooler 16, to the top of the 'adsorbersectionproper, being intro-' duced at a point between the clean-upsection and adsorber section 3. The balance or minor portion of thepartially desorbed solid is introduced via line I2 into a clean-updesorber i3 equipped with heating coils I4. Into the bottom of vessel i3there is introduced under pressure via line I5 wash liquid C which isintroduced in sufficient volume to physically desorb substantiallycompletely component B from the solid by a washing action. This washliquid which has substantially completely stripped component B from thesolid is then introduced, in toto, via line S to partial desorber 8wherein it contacts the total solid stream in a partial desorptionoperation as related above. The completely desorbed solid which nowpossesses its complete adsorbing capacity for component B is removedfrom clean-up ydesorber via line Il with lift liquid via line 22, cooledin cooler I8 and introduced `via line i9 into the top of the clean-upadsorber section 5. This solid acts to pick up any component B whichthrough incomplete adsorption or otherwise enters the light liquid andtends to pass overhead therewith.

Now, the bulk of the wash liquid C is removed with the product B vialine Ill.,v However, each of the circulating solid streams introducedinto the upper section of the vessel I .via lines i I and i9 containcertain amounts of component C. Since this component is lighter boilingthan A and B and since it is less adsorbable than these components itpasses overhead from Vessel I through line 20 with unadsorbed componentA. This liquid is sent to a fractionator not shown for separation of Aand C. The latter is returned to the system Via line I5.

The system described is adequately suitable for the separation ofheptane (B) from isooctane (A) using charcoal as the solid adsorbent andemployingpentane (C) as the wash liquid. Simi-y larly, toluene (B) isseparated from a mixture with methyl cyclohexane (A) employing silicagel as the adsorbent and hexane or pentane as the wash liquid.

Although the liquid-solid system has been described for separating amixture of two componente, three or more fractions can be recovered froma mixture containing them by providing one or more sidestream productwithdrawal points as illustrated in Figure 1. Likewise the process ofFigure l is operated to separate more than three components by providingadditional spaced sidestream draw-offs from rectification sections invessel l.

As previously recited in connection with the discussion of the processof Figure l it should be borne in mind that it is possible to combinevessels I, 8 and I3 into a single unitary Without entailing any changesin this phase of the invention.

Cooling of the recycled adsorbent streams may be effected within theadsorber near the points of solids entry by means of coils containedVtherein. Also, as a preferred means of heating and cooling the solid,liquid may be withdrawn from the vessels at appropriate points, heatedor cooled externally, and readmitted to the adsorber or desorbers atlower points to eifect the desired heating or cooling. Heating andcooling means, however, do not comprise a part of the present invention.

in each of the processes illustrated 'by the drawings the vapor productsand liquid products withdrawn from the appropriate vessels are con- 81taminated with impurities such as water, entrained solids, etc. Theseimpurities are removed by conventional means such as water scrubbing,filtering, centrifuging, passage through cyclone separation or settlingZones, etc. and do not constitute any part of this invention.

It is also to be understood that during the adsorption-desorption cyclesome of the adsorbent will become deactivated thus requiringregeneration. The latter is also carried out by conventional means suchas withdrawal of a fraction of the solid preferably from the desorbedstream and subjecting it to higher temperatures, i. e. to temperaturesin the range of 70021600 F., and to the action of stripping gases, e. g.steam, flue gas, CO2, etc. to remove deactivants. Thus, a stream ofdesorbed adsorbent is removed from line Il' and sent to reactivator 31via pipe 3b. Steam or other reactivating gases, as previously mentioned,enters vessel 31 via line 38 and at the temperatures employed, namely,approximately 700 F. to 1600 F., strips deactivants such as polymericmaterials from the adsorbent. The reactivating gases and deactivants areremoved from the Vessel via line 39 and the reactivated char is removedfrom the vessel via line ii. The latter is cooled and employed again inthe main adsorption process or in the tail gas scrubber.

When the system is operated employing a fluidized adsorbent in theadsorbent tower the adsorbent is handled as a dense fluid bed in whichthe particles average approximately 50- 230 micron particle size. Theparticles possess considerable'motion relative to each other and platesor packing are required in the tower in order to eifect sufficientcountercurrent contact between the adsorbent and vapor. The tower may besupplied with perforated plates equipped with simple standpipeoverflows, the vapor passing upwardly through the plate perforations ata velocity sufficiently high to prevent downward passage of charcoaltherethrough, and to provide good solids fluidization. Packing or bubblecap plates can also be employed. Approximately l to 3 feet of dense bedand 2 feet of vapor disengaging space per plate are adequate toestablish a satisfactory approach to equilibrium between Vapor andsolid, In the moving-bed type of operation the feed gas is fed to thetower at a point near the center thereof. The tower is packed with anadsorbent of approximately 10 to 30 mesh in size which in the case ofcharcoal would amount to a bulk density of about 30 lbs. per cu. ft. Thetower is operated under a pressure of about 50 to 100 p. s. i. g., forexample. The packed adsorbent gravitates at a predetermined rate fromthe top to the bottom of the tower as previously described.

The charcoal inventory in a tower of a given diameter and height is muchsmaller when the adsorbent is fluidized than when it is handled as amoving bed, and uidized solids permit much higher tower vaporvelocities. Also much higher heat transfer coeificients are obtained.with iiuidized solids than with close packed solids.

The invention is generally applicable to fractionation processes of thetype illustrated above, involving selective adsorption of one or morecomponents from a mixture containing other components which are more andless readily adsorbed. In such operations it may be used to separatehydrocarbon mixtures into fractions of any desired boiling range orchemical structure by suitable selection of adsorbents and strippingagents in conformity with chromatographic principles. For example,parafnns, naphthenes, oleiins, diolefins and aromatics may be obtainedas separate fractions from mixtures of two or more of these classes ofhydrocarbons with a silica gel adsorbent used in an adsorption processas described above in one or more stages according to the number offractions to be separated. Similarly, organic vapors of differentdegrees of polarity may also be separated by selective adsorption on anysuitable solid adsorbent.

The process is particularly applicable to the recovery of `C2 and `C3hydrocarbons from refinery fuel gas; to the recovery of light ends fromlow pressure catalytic cracking gases; to the recovery of hydrocarbonsand oxygenated compounds from hydrocarbon synthesis gas produced at lowpressures; to the separation of methane from nitrogen; to the recoveryof acetylene from the gases of the Wulff process; to the drying of lightgases and air, and to the recovery of valuable solvents such as benzenefrom gases containing it.

What is claimed is:

1. In a cyclic process for the separation of a,

fluid mixture containing a less readily adsorbed component A and a morereadily adsorbed component B by'means of adsorption on a solid adsorbentin an adsorption Zone in which Ythe fluid mixture is countercurrentlycontacted with the adsorbent to adsorb component B, a fluid stream Ycomprising components A and B removed from the adsorption zone, theadsorbent containing component B desorbed to release component Btherefrom, and the desorbed adsorbent returned to the adsorption zone,the improvement which comprises partially desorbing component B from thetotal adsorbent in a partial desorption zone, completely desorbingcomponent B from a minor portion of the adsorbent in a clean-updesorption zone, returning the partially desorbed 'adsorbent to theadsorption zone, and scrubbing the fluid stream comprising components Aand B in a scrubbing zone with the completely desorbed adsorbent toassure complete removal of component B from component A.

2. A process according to claim 1 in which the desorption in both zonesis carried out by steam stripping.

3. A process according to claim 1 in which the adsorbent is removed fromthe scrubbing Zone and introduced into theadsorption Zone.

4. A process according to claim 1 in which the fluid mixture is a liquidmixture in which component A is methyl cyclohexane and component B istoluene, and in which the solid adsorbent is silica gel.

5. A process according to claim 1 in Which the fluid mixture contains amixture of hydrocarbons in which component A is 4C2 hydrocarbons andless adsorbable gases and component B is predominantly `Ca andy C4hydrocarbons.

6. A process according to claim 1 in Which the fluid mixture is agaseous mixture containing hydrocarbons in which component A is C2hydrocarbons and less adsorbable gases and component B is predominantlyC3 hydrocarbons.

7. A process according to claim 1 in Which the adsorbent isactivatedcarbon and in which a portion of the carbon from the clean-updesorption zone is fed to a high temperature regeneration Zone.

8. A process for the separation of a fluid mixture comprising a lessreadily adsorbed component A, a more readily adsorbed component C and anintermediate component B by means of adsorption by a solid adsorbentwhich comprises passing said adsorbent downwardly through a contactingzone having an adsorption section above a iiuid mixture feed-point and arectification section below said feed-point, feeding the fluid mixtureto a lower portion of the adsorption section to adsorb components B andC, removing a fluid stream comprising unadsorbed components A and B froman upper portion of the adsorption section, refiuxing the adsorbent inthe rectification section with a fluid comprising component C introducedat a lower section of the rectification section, removing a fluid streamcomprising components B and C from an upper portion of the rectificationsection, passing the adsorbent downwardly from the rectification sectioninto a partial desorption zone, partially desorbing component C from thetotal adsorbent in the partial desorption zone with the aid of astripping medium introducedfrom a clean-up desorption Zone, removing afluid stream comprising component C from the partial desorption zone,passing a minor portion of the adsorbent from the partial desorptionzone into a clean-up desorption zone, completely desorbing component Cfrom the adsorbent in the clean-up zone by stripping it with a strippingmedium introduced into the clean-up desorption zone, returning thepartially desorbed adsorbent from the partial desorption zone to theadsorption zone, and scrubbing at least one of the fluid streamscomprising components A and B and components B and C respectively in ascrubbing Zone with the completely desorbed adsorbent.

9. A process according to claim 8 in which the fluid stream comprisingcomponent A is scrubbed with the completely desorbed adsorbent and theadsorbent returned from the scrubbing zone to the adsorption section.

10. A process according to claim 8 in which the fluid stream comprisingcomponent B is scrubbed with the completely desorbed adsorbent and theadsorbent returned from the .scrubbing zone to the rectificationsection.

11. A process according to claim 8 in which the fluid mixture comprisesa hydrocarbon mixture in which component A is methane and lessadsorbable gases such as nitrogen, carbon monoxide and hydrogen,component B is C2 hydrocarbons, and component C is C3 and heavierhydrocarbons, and in which the adsorbent is activated carbon.

ROBERT P. CAHN. LEWIS D. ETHERINGTON.

References Cited in the le of this patent UNITED STATES PATENTS NumberName Date 1,830,178 Speer J1'. Nov. 3, 1931 1,836,301 Bechthold Dec. 15,1931 2,519,342 Berg Aug. 22, 1950 2,523,149 Scheeline Sept. 19, 19502,529,289 Gilliland Nov. Y, 1950 2,630,877 Berg Mar. 10, 1953 OTHERREFERENCES Publication, Hypersorption Light Gases, by Clyde Berg,Transactions of A. I. Ch. E., August 25, 1946, pp. 665-680.

1. IN CYCLIC PROCESS FOR THE SEPARATION OF A FLUID MIXTURE CONTAINING ALESS READILY ADSORBED COMPONENT A AND A MORE READILY ADSORBED COMPONENTB BY MEANS OF ADSORPTION ON A SOLID ADSORBENT IN AN ADSORPTION ZONE INWHICH THE FLUID MIXTURE IS COUNTERCURRENTLY CONTACTED WITH THE ADSORBENTTO ADSORB COMPONENT B, A FLUID STREAM COMPRISING COMPONENTS A AND BREMOVED FROM THE ADSORPTION ZONE, THE ADSORBENT CONTAINING COMPONENT BDESORBED TO RELEASE COMPONENT B THEREFROM, AND THE DESORBED ADSORBENTRETURNED TO THE ADSORPTION ZONE, THE IMPROVEMENT WHICH COMPRISESPARTIALLY DESORBING COMPONENT B FROM A MINOR THE TOTAL ADSORBENT IN APARTIAL DESORPTION ZONE, COMPLETELY DESORBING COMPONENT B FROM A MINORPORTION OF THE ADSORBENT IN A CLEAN-UP DESORPTION ZONE, RETURNING THEPARTIALLY DESORBED ADSORBENT TO THE ADSORPTION ZONE, AND SCRUBBING THEFLUID STREAM COMPRISING COMPONENTS A AND B IN A SCRUBBING ZONE WITH THECOMPLETELY DESORBED ADSORBENT TO ASSURE COMPLETE REMOVAL OF COMPONENT BFROM COMPONENT A.